This invention relates to the manufacture of semiconductor devices and circuits and more particularly to an apparatus and method for scribing semiconductor wafers.
After devices or circuits are fabricated on a semiconductor wafer, the individual devices or circuits are usually separated from each other by sawing with a diamond-coated saw blade or by scribing the wafer with a sharply pointed diamond scribe and fracturing the wafer along the scribed lines. In certain types of devices or semiconductor materials, scribing and cleaving is the preferred method of separating the individual units on the semiconductor wafer.
In order to scribe a semiconductor wafer, the diamond scribe tip is placed on the surface of the wafer near the distal edge of the wafer and the wafer and diamond scribe tip are moved laterally relative to each other for a distance equal to the entire width of the wafer, forming a scribe line. The diamond scribe tip is raised from the surface of the wafer and the diamond scribe tip and the wafer are indexed relative to each other in the direction perpendicular to the scribe line for a distance equal to the width of an individual device. The diamond scribe tip is again placed on the surface of the wafer and the wafer and the wafer and diamond scribe tip are moved laterally relative to each other again for a distance equal to the entire width of the wafer forming a second scribe line. This process continues until the proximal edge of the wafer surface is reached. The wafer is then rotated 90 degrees and the process described above is repeated.
Current apparatus used to scribe semiconductor wafers provide the motion of the diamond scribe tip relative to the surface of the wafer by holding the diamond tip fixed in one or both lateral directions and moving the table on which the wafer is mounted in one or both of the lateral directions. This approach is evident in Kulicke, U.S. Pat. No. 3,094,785, and Turner, U.S. Pat. No. 5,820,006. This method worked well when semiconductor wafers were small. However, as the wafer diameters have gotten much larger, to 200 mm and 300 mm diameter, the size and weight of the mechanism needed to move the larger table holding the wafer has increased dramatically. This makes it difficult to precisely control the position of the diamond scribe tip relative to the surface of the wafer and requires slowing the motion of the mechanism in order to maintain adequate control.
One of the most important process parameters in achieving a successful scribe line in the surface of the wafer, which in turn results in a successful cleave, is the scribe force applied to the diamond scribe tip. Several different methods have been used to control the scribe force in different scribe apparatus. Kulicke, in U.S. Pat. No. 3,094,785, uses changeable weights acting on the scribe arm that in turn applies force to the scribe tip. Lin, in U.S. Pat. No. 4,502,225, uses a series of levers and springs to apply the scribe force. Other apparatus use air pressure acting on the scribe arm to control the scribe force. Turner, in U.S. Pat. No. 5,820,006; describes a method of electronically controlling the scribe force by using a load cell mounted in a voice coil. Since load cells are analog devices, this approach will not work well, as the electrical noise from the motor drive system will interfere with the analog output from the load cell.
The purpose of this invention to provide a system to scribe semiconductor wafers, in order to separate them into individual devices, that provides more precise control over the motion of a diamond scribe tip relative the surface of a semiconductor wafer. The second purpose of this invention is to provide a system to precisely control the scribe force applied between the diamond scribe tip and the surface of the wafer.
Unlike prior art, in apparatus constructed in accordance with the teachings of the present invention, the rotary stage, on which the semiconductor wafer is held, is rigidly affixed to a base plate. The diamond scribe tip is moved relative to the surface of the wafer using a gantry arrangement whereby motion stages using linear motors and linear encoders are used to precisely position the diamond scribe tip relative to the surface of the wafer. In this configuration the weight of the moving portion of the apparatus is much less than in prior art. This allows the stages to be moved faster and with more precision. This results in better control of the characteristics of the scribe line and higher wafer throughput for greater manufacturing efficiencies.
The force applied to the surface of the semiconductor wafer by the scribe tip is measured and controlled by a unique structure. The measurement of the force is accomplished using a plurality of flexible beams whose deflection is measured precisely using a linear encoder. The applied force is controlled using a linear motor that is part of a vertical motion stage that supports the force measuring apparatus.
Other features, advantages and objects of the present invention will become apparent with reference to the following description and accompanying drawings.